Effect of thrombin on p42/44, p38 MAPK, and Jun kinase activities in different Jurkat clones. Cells were stimulated with 100 nmol/L thrombin for the times indicated. Cell lysates were prepared as described in Materials and Methods and incubated overnight with anti-p42/44 MAPK (A) , anti-p38 MAPK (B), or anti-JNK antibodies (C) preadsorbed to protein A-Sepharose. Immune complexes were washed and kinase activities were determined using myelin basic protein for p42-44 MAPK and ATF2-GST for p38 MAPK and JNK. Equal amounts of p42/44 MAPK and p38 MAPK were immunoprecipitated in each condition (A and B, bottom).